In solidity, the modifier is used to change the behavior of a function. They can automatically check a condition prior to executing the function. Here is an example, as follows:

pragma solidity ^0.4.24;
contract Modifiers {
         address public admin;
    function construct () public {
       admin = msg.sender;
    }
    //define the modifiers
    modifier onlyAdmin() {
        // if a condition is not met then throw an exception
        if (msg.sender != admin) revert();
        // or else just continue executing the function
        _;
    }
    // apply modifiers

    function kill() onlyAdmin public {
         selfdestruct(admin);
    }
}